ACTG 345 is a phase I/II trial to assess the safety, tolerance, pharmacokinetics, and activity of ritonavir alone and in combination with 3TC and ZDV in HIV-infected infants and children. Subjects are stratified by the following age groups: Group I: >6 months to 2 years; Group II: 3 months to 6 months; Group IIIA: 4 weeks to < or equal to 10 weeks; and Group IIIB: 1 month to < 3 months. Since the study opened here at The Children's Hospital of Philadelphia (CHOP), one child has been enrolled. This child has not experienced any adverse events. This child will continue to be followed as per the study protocol. Currently, enrollment is closed pending the next version of the protocol. We anticipate that the protocol will be submitted to the IRB in April and pending approval will re-opened for enrollment of patients at CHOP.